US3889776A

US3889776A - Exhaust gas silencer

Info

Publication number: US3889776A
Application number: US383226A
Authority: US
Inventors: Peter Postma
Original assignee: Sherritt Gordon Mines Ltd
Current assignee: Viridian Inc Canada
Priority date: 1973-06-14
Filing date: 1973-08-21
Publication date: 1975-06-17
Anticipated expiration: 1992-06-17
Also published as: AU6994574A; FI173974A; FR2233495A1; DE2428837A1; CA980258A; PH12305A; FR2233495B1; JPS5022135A; FI56578C; ZA743160B; GB1464440A; FI56578B

Abstract

A completely open gas silencer is disclosed, which comprises an elongated hollow baffle casing having an open end and a closed end. An inlet conduit is attached to the closed end of the baffle casing. An end portion of the inlet conduit extends into the baffle casing. This end portion is coaxially encircled by a hollow cylinder having a plurality of perforations formed on its cylindrical wall. A filter cap is removably mounted on the hollow cylinder and located transversely and directly opposite to the end opening of the inlet conduit. A porous member is mounted in the filter cap to break up the exhausted noisy gas into a number of random gas streams in order to reduce the gas velocity. A lining of sound absorbing material is disposed on all inside walls of the baffle casing to absorb the noise in the random gas streams.

Description

United States Patent 1 91 Postma 1 EXHAUST GAS SILENCER [75] Inventor:

[7 3] Assignee: Sherritt Gordon Mines Limited,

Fort Saskatchewan, Canada 221 Filed: Aug. 21, 1973 21 Appl. No.: 383,226

Peter Postma, Toronto, Canada [30] Foreign Application Priority Data June 14, 1973 Canada 174021 152] US. Cl l8l/50; 18/55 M [51] Int. Cl. ..F01n 1/10 [58] Field of Search 181/35 R, 35 C, 36 R, 36 B, 181/47 R, 41, 42, 49, 50,55, 61, 68, 71, 72

9/1969 Vegcby 181/55 3,698,510 10 1972 Blattct a1. 181/50 x FOREIGN PATENTS OR APPLICATIONS 20,266 6/1915 Denmark ..1s1 s5 1.224.400 4/1959 France 181/56 Primary Examiner-Richard B. Wilkinson Assistant ExaminerVit W. Miska Attorney, Agent, or Firm-Frank 1. Piper; Arne I. 'Fors -[57] ABSTRACT I A completely open gas silencer is disclosed, which comprises an elongated hollow baffle casing having an open end and a closed end. An inlet conduit is attached to the closed end of the baffle casing. An end portion of the inlet conduit extends into the baffle casing. This end portion is coaxially encircled by a hollow cylinder having a plurality of perforations formed on its cylindrical wall. A filter cap is removably mounted on the hollow cylinder and located transversely and directly opposite to the end opening of the inlet conduit. A porous member is mounted in the filter cap to I break up the exhausted noisy gas into a number of random gas streams in order to reduce the gas velocity. A lining of sound absorbing material is disposed on all inside walls of the baffle casing to absorb the noise in the random gas streams.

10 Claims, 3 Drawing Figures WWHWQ SOUND PRESSURE LEVEL IN THE GIVEN OCTAVE BAND (DECIBELS REFERRED TO 0.0002 DYNES PER 50. CM.)

PATENTEDJUN 17 ms 3,889,776

VV /WWW D I cg 310,0, C C =C kjixv 28 '11 14 13 FIG. 1 i\ 16-L i w|T|-|ouT SILENCER 9o- WITH SILENCER m 70- BACKGROUND NOISE TAKEN 40 WITH VENT SHUT s3 15 25o 5'00' 1obo' 2600'40'00' 8600 MID-POINT FREQUENCY OF OCTAVE ANALYSED(CYCLES PER SECOND) EXHAUST GAS SILENCER This invention relates to gas exhaust silencersfor subduing the noise of a gas exhaust-to an acceptable sound level.

In an industrial environment. machinery and other industrial systems and processes produce continuous noise. Such noise may cause damage to the hearing of the workers who are exposed to the noise over a long period of time. The damage may be permanent or of a temporary nature depending on the hearing threshold and tolerance of the individual.

The loudness of a sound depends on the sound energy it possesses and it is commonly measured by its sound pressure level in decibel (db). which is a measure of the root-mean-square value of the instanta neous sound pressure at a point with respect to a reference sound pressure. The unit of the sound pressure is the microbar or dyne per square centimeter. The standard reference sound pressure is 0.0002 microbar. Sounds in different frequencies generate different sound pressuresfThe average individual is able to hear and distinguish a sound in the frequency range of from 60 cycles per second to about 15,000cycles per second. The sound pressure level of an environment is measured in octave frequency bands within this audible frequency range to determine its loudness. It has been established that the safe threshold of sound pressure level in any one critical sound frequency band is approximately 85 db re 0.0002 microbar.

In industrial plants many high pressure gas exhausts may produce intolerable loud noise due to the high vibration of the air medium when it is ejected through the exhaust pipe or system. It has been known to attach a silencer to the exhaust pipe to attenuate the noise to an acceptable level below 85 db. Noise attenuation in the silencer may be accomplished by the reflection of energy back into the source or by absorption of the energy with energy absorption structures. However, known silencers are complicated in structure and are expensive to fabricate.

Known silencers also have a closed structure in which the silencer is in the form of a fully enclosed baffle chamber. The interior of the baffle chamber is divided into a plurality of complicated maze-like partitions which include various sound absorbing and reflecting structures. The outlet end of the baffle chamber is usually closed by sound absorbing material, so that the interior of the baffle chamber is inaccessible for repair and/or replacement. Some silencers such as automobile mufflers have a somewhat open outlet. However, the area accessible through the open outlet is completely isolated from the other interior structures and such outlet is usually extremely small in dimension in order to provide a maximum reflection of the gas exhaust back into the baffle chamber. Therefore, it is essentially a closed structure. One disadvantage of the closed structure of the known silencers is that condensation of moisture and accumulation of suspended particles carried in the exhausted gas tend to clog up the interior of the silencer to render it ineffective and eventually inoperative. Often. the interior of the silencer is still in good structural condition yet due to the closed structure, it is time consuming and economically not feasible to repair such closcd silencers. Therefore, they must be replaced in whole.

It is a principal object of the present invention to provide a silencer which is effective in attenuating the noise of an air exhaust to below db sound pressure level.

It is another object of the present invention to provide a silencer which is simple in structure.

A further object of the present invention is to provide a silencer which is of an open structure in which the interior ofthe silencer is fully accessible for maintenance purposes.

It is to be understood that the term air used in the present description includes gas and gas-like discharge through an exhaust. which may have a moisture content and/or particle suspension.

According to the present invention, the gas exhaust silencer comprises an elongated hollow baffle casing having an open end and a closed end. an inlet conduit attached to said closed end of said baffle casing and having an end portion extending into said baffle casing. a hollow cylinder located in said baffle casing and coaxially encircling said end portion of said inlet conduit in a spaced relation therewith, a filter cap member removably mounted on said hollow cylinder and disposed transversely and directly opposite to the end opening of said inlet conduit. a porous member mounted in said filter cap member, and a lining of sound absorbing materialdisposed on all inside walls of said baffle casing.

A specific embodiment of the invention will now be described with reference to the accompanying drawings. in which:

FIG. I is a side sectional elevation of the air exhaust silencer;

FIG. 2 is a top sectional elevation of an air exhaust silencer taken along line 22 in FIG. I; and

FIG. 3 is a graph showing the effect of the silencer in alternating noise in the audible frequency range.

The silencer comprises a hollow baffle casing 10. The baffle casing may have a circular or other conventional shape in its transverse cross-section and has a closed end II and an open end 12. An inlet conduit 13 is mounted on the baffle casing 10 through the centre of the closed end 11. A short length of the end portion of the inlet conduit extends into the baffle casing as shown in FIG. I. The cross-sectional diameter of the baffle casing is substantially larger than the cross-sectional diameter of the inlet conduit. For example, the diameter of the baffle casing is about 10 inches and the diameter of the inlet conduit is about 1 inch. The inlet conduit may be welded to the closed end of the baffle casing at 14. The inlet conduit is attachable to a noisy gas or air exhaust pipe 15. The noise produced by the gas exhaust may be due to high velocity gas being exhausted through the pipe causing the gas medium to vibrate violently. A set screw such as an L-shaped clamping screw 16 may be used to fasten the conduit to the air exhaust pipe or a flanged connection may be provided to mount the inlet conduit to the air exhaust pipe in a well known manner.

A hollow cylinder 17 is disposed within the baffle casing 10 and coaxially encircles about the end portion of the inlet conduit and is in a spaced relation therewith. The hollow cylinder 17 has a dimension substantially larger than the inlet conduit. With an inlet conduit having a 1 inch diameter as mentioned above, the diameter of the hollow cylinder may be 6 inches. The wall of the hollow cylinder 17 is perforated with a plurality of openings 18. One end of the hollow cylinder 17 is removably secured to the closed end of the baffle casing by means of studs 20 and nuts 2|.The other end of the hollow cylinder is disposed about thesame height as and preferably slightly belowthe end of the inlet conduit. A porous member such as a thick gauze pad 22 is mounted transversely and directly opposite to the end opening of the inlet conduit 13 by a wire mesh 23 in the shape of a cap which is removably mounted on the rim of the end of the hollow cylinder such as by screws 24. The wire mesh 23 and the gauze pad 22 form a filter cap which co-operate with the -hollow cylinder l7 and the closed end of the baffle casing H) to form a filter casing surrounding over and around the inlet conduit in the baffle casing.

The inside walls of the baffle casing 10 are lined with a sound absorbing material 25 having a sound permeable cellular structure such as fibre glass, metal gauze or lathe turnings. The sound absorbing material may be adhered to the inner walls of the baffle casing or alternatively a stiff porous mask such as a galvanized wire screen 26 may be used to removably retain the sound absorbing material in place. A frusto-conical shaped divergent rim 27 is attached to the open end ofthe baffle casing 10. At least one hole 28 may be formed in the closed end in the space between the hollow cylinder 17 and the lining of sound absorbing material 25 to serve as weep holes for dispensing any liquid condensation or matters from the baffle casingssuch weep holes are spaced evenly around the closed end.

The high velocity exhausted gas enters the baffle casing through the inlet conduit 13. The exhausted gas carries with it the energy which can create sound vibrations. When the gas enters the hollow cylinder through the inlet conduit it will expand initially since the hollow cylinder is relatively much larger than the inlet conduit. This initial expension will slow down its velocity slightly. However, due to its momentum it will continue to travel towards the filter cap, thus. it impinges directly on the gauze pad 22. The initially expanded gas is then divided into a plurality of small low velocity streams by passing through the much larger area of the gauze pad and the numerousair spaces in the wire mesh 23. The streams enter the baffle casing in various random directions. Hence, the velocity of the incoming gas is drastically reduced to the extent that it loses the energy to vibrate the surrounding gas mass. Should the mesh or gauze pad become plugged through contained impurities, the gas will to pass through the plurality of openings 18 formed on the walls of the hollow cylinder. The openings again serve to reduce the velocity of the gas and thus they serve as sound attenuating filters which absorb the sound energy as the exhausted gas passes therethrough. It will be understood that no back pressure is manifested in the hollow cylinder since the initially expanded gas can pass readily through the gauze pad 22 or the openings 18.

The gauze pad and the hollow cylinder also serve to change the direction of the exhausted gas, so that the gas after being filtered by the gauze pad and the openings of the hollow cylinder is broken up into various components which enter the baffle casing in various radial directions. The breaking of the directivity of the sound wave emanating from the exhaust. pipe further reduces the sound energy in the exhaustedgas. The broken gas streams or components entering the baffle casing will impinge on the sound absorbing material or lining in various random directions, and the remaining sound energy in these gas streams or components is thus absorbed by the sound absorbing material.

A small number of the gas components after passing through the gauze pad and the wire mesh 23 may travel directly towards the open end without impinging on the sound absorbing material of the baffle casing. However. gas components moving in this direction have extremely small velocity and sound energy and a large portion of the sound energy therein will be dissipated by expansion in the large space of the baffle easing-as well as in the large space defined by the divergent rim 27 before they reach the open end.

It is apparent from the above description that. the velocity of the exhausted gas is greatly reduced as it passes through the gauze .pad, the wire mesh and the openings of the hollow cylinder yet it produces noback pressure in the silencer. The reduction of the gas velocity eliminates the vibration of the gas medium that produces the sound. The frusto-conical rim 27 located at the open end of the baffle casing serves as an expansion baffle to slow down the velocity of the gas components which may reach the open end of the baffle casing, and

to deflect any sound generated in an upward direction.

In the above manner. the velocity of the noisy exhausted air or gas from the exhaust pipe is drastically reduced by the silencer to eliminate any further production of noise and the existing sound energy the range of 63 cps to 8,000 cps is taken. The results show that the silencer is effective in attentuating all sound energy in the various frequency bands to far below the i db maximum acceptable level. The curve measured with the silencer attached to the exhaust pipe falls almost exactly on the curve of the ambient noise measured with the exhaust pipe completely shut off. l

It should be obvious that the silencer according to the v present invention is simple in structure and due to its open structure, replacement and cleaning of the components can be made easily and quickly.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be'made I therein without departing from the spirit and scope of the invention.

What I claim as new and desire to protect by Letters Patent of the United States is:

1. An open end gas exhaust silencer comprising an elongated 'hollow baffle casing having a fully open end and a closed end, an inlet conduit secured to said closed end of said baffle casing and having an end portion therein extending into said baffle casing through said closed end, said inlet conduit being operative to be connected to a noisy gas exhaust pipe having an exally encircling said end portion of said inlet conduit in a spaced relation therewith, the side wall of said hollow cylinder being entirely full of perforations, a filter cap member removably mounted on said hollow cylinder and disposed transversely and directly opposite to the end opening of said inlet conduit, said filter cap in combination with said hollow cylinder defining a space considerably smaller than the remaining hollow space in said baffle casing. a porous element mounted in said filter cap member operative for dividing the exhausted gas into a plurality of random gas streams so as to reduce the velocity of the exhausted gas whereby eliminating the noise in said exhausted gas. and a lining of sound absorbing material disposed on all inside walls of said hollow baffle casing for absorbing any remaining noise in said random gas streams.

2. An open end gas exhaust silencer according to.

claim 1 in which said hollow baffle casing has a crosssectional dimension substantially larger than the crosssectional dimension of said inlet conduit.

3. An open end gas exhaust silencer according to claim 2 in which said sound absorbing material has a sound permeable cellular structure.

4. A gas exhaust silencer according to claim 3 in which said sound absorbing material is fibre glass. metal gauze or lathe turningsr 5. An open end gas exhaust silencer according to claim 3 including a frusto-conical shaped divergent rim located at the open end of said baffle casing.

6. An open end gas exhaust silencer according to claim 5 including a stiff porous mask located in said baffle casing to removably retain said lining of sound absorbing material therein.

7. An open end gas exhaust silencer according to claim 6 including at least one weep-hole formed in the closed end of said baffle casing.

8. An open end gas exhaust silencer according to claim 7 wherein said porous member is a gauze pad made of material suitable for the'gas or vapour to be exhausted.

9. An open end gas exhaust silencer according to claim 8 wherein said filter cap member is a wire mesh having numerous air spaces therein.

10. An open end gas exhaust silencer suitable for attenuating the noise of an exhausted gas and the like comprising an'elongated hollow baffle casing having a fully open end and a closed end, an inlet conduit secured to said closed end of said baffle casing and having an end portion therein extending into said baffle casing, said inlet conduit having an outside end operative to be connected to a noisy gas exhaust pipe having said exhausted gas releasing therefrom in a high velocity. a hollow cylinder located in said baffle casing and coaxially encircling said end portion of said inlet conduit in a spaced relation therewith, said hollow cylinder having a cross sectional diameter substantially larger than said inlet conduit but substantially smaller than that of said baffle casing, the side wall of said hollow cylinder being entirely full of perforations, one end of said hollow cylinder being removably secured to the closed end of said baffle casing and the other end of said hollow cylinder being spaced from the end opening of said inlet conduit, a filter cap member removably mounted on said other end of said hollow cylinder and disposed in a transverse spaced manner directly opposite to the end opening of said inlet conduit, said filter cap member and said hollow cylinder co-operating with said closed end of said baffle casing to form a filter cas ing covering over and encircling around the end portion of said inlet conduit and operative for providing an initial expansion chamber for said exhausted gas. said casing defining a space considerably smaller than the remaining hollow space of said baffle casing. a porous element mounted in said filter cap member and disposed in a spaced relation to the end opening of said inlet conduit and operative for dividing the exhausted gas into a plurality of random gas streams having low velocities and entering said hollow baffle casing in random radial directions. and a lining of sound absorbing material disposed on all inside walls of said baffle casing for absorbing any remaining noise in said random gas streams.

Claims

1. An open end gas exhaust silencer comprising an elongated hollow baffle casing having a fully open end and a closed end, an inlet conduit secured to said closed end of said baffle casing and having an end portion therein extending into said baffle casing through said closed end, said inlet conduit being operative to be connected to a noisy gas exhaust pipe having an exhausted gas releasing therefrom in a high velocity, a hollow cylinder located in said baffle casing and coaxially encircling said end portion of said inlet conduit in a spaced relation therewith, the side wall of said hollow cylinder being entirely full of perforations, a filter cap member removably mounted on said hollow cylinder and disposed transversely and directly opposite to the end opening of said inlet conduit, said filter cap in combination with said hollow cylinder defining a space considerably smaller than the remaining hollow space in said baffle casing, a porous element mounted in said filter cap member operative for dividing the exhausted gas into a plurality of random gas streams so as to reduce the velocity of the exhausted gas whereby eliminating the noise in said exhausted gas, and a lining of sound absorbing material disposed on all inside walls of said hollow baffle casing for absorbing any remaining noise in said random gas streams.

2. An open end gas exhaust silencer according to claim 1 in which said hollow baffle casing has a cross-sectional dimension substantially larger than the cross-sectional dimension of said inlet conduit.

4. A gas exhaust silencer according to claim 3 in which said sound absorbing material is fibre glass, metal gauze or lathe turnings.

5. An open end gas exhaust silencer according to claim 3 including a frusto-conical shaped divergent rim located at the open end of said baffle casing.

8. An open end gas exhaust silencer according to claim 7 wherein said porous member is a gauze pad made of material suitable for the gas or vapour to be exhausted.

10. An open end gas exhaust silencer suitable for attenuating the noise of an exhausted gas and the like comprising an elongated hollow baffle casing having a fully open end and a closed end, an inlet conduit secured to said closed end of said baffle casing and having an end portion therein extending into said baffle casing, said inlet conduit having an outside end operative to be connected to a noisy gas exhaust pipe having said exhausted gas releasing therefrom in a high velocity, a hollow cylinder located in said baffle casing and coaxially encircling said end portion of said inlet conduit in a spaced relation therewith, said hollow cylinder having a cross sectional diameter substantially larger than said inlet conduit but substantially smaller than that of said baffle casing, the side wall of said hollow cylinder being entirely full of perforations, one end of said hollow cylinder being removably secured to the closed end of said baffle casing and the other end of said hollow cylinder being spaced from the end opening of said inlet conduit, a filter cap member removably mounted on said other end of said hollow cylinder and disposed in a transverse spaced manner directly opposite to the end opening of said inlet conduit, said filter cap member and said hollow cylinder co-operating with said closed end of said baffle casing to form a filter casing covering over and encircling around the end portion of said inlet conduit and operative for providing an initial expansion chamber for said exhausted gas, said casing defining a space considerably smaller than the remaining hollow space of said baffle casing, a porous element mounted in said filter cap member and disposed in a spaced relation to the end opening of said inlet conduit and operative for dividing the exhausted gas into a plurality of random gas streams having low velocities and entering said hollow baffle casing in random radial directions, and a lining of sound absorbing material disposed on all inside walls of said baffle casing for absorbing any remaining noise in said random gas streams.